1. Field of the Invention
The present invention relates to sound absorbing structures for use in underwater applications.
2. History of the Prior Art
The present technology has provided a variety of different designs and constructions of sound absorbing panels and similar structures for use in various different applications. However in the case of underwater applications, the choice is highly limited due to the problem of providing a panel or structure which can withstand the high pressures present in most underwater applications. For example it is known to cover the hulls of naval underwater vessels with sound absorbing material for the purpose of absorbing energy waves within the water such as a SONAR signal transmitted by an enemy vessel.
However current acoustical panels and materials have proven to be undesirable or unsatisfactory for underwater applications in which relatively high water pressures are involved. In these instances, the sound absorbing material is mounted on the hull of the vessel or otherwise disposed so as to be directly exposed to the water. The high water pressure results in substantial compression of the material so as to severly limit its sound absorbing capabilities. In addition the high degree of compression may alter the buoyancy and other properties of the sound absorbing material to an undesirable extent.
To avoid these problems inherent in direct exposure of acoustically absorbent material to the water and its pressure, one approach has been to consider the use of a housing of the type which would transmit sound to the sound absorbent material stored therein while at the same time being capable of withstanding the high water pressure so as to prevent compression of the sound absorbing material. While this approach has appeared to hold considerable promise from a theoritical basis, it has gone unfulfilled because of the problems inherent in designing a structure which will withstand the high water pressures and at the same time act as a housing with good acoustical transmission to the interior thereof.